Browse Prior Art Database

Trench Capacitor Modification to Improve Storage Time

IP.com Disclosure Number: IPCOM000112555D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Katcoff, DL: AUTHOR [+4]

Abstract

In one device capacitor storage memory cells made with trench storage capacitor technology, failure of capacitor cells to hold or retain stored charge has been correlated to the presence of crystal defects emanating from the capacitor trenc h wall and passing through the P-N node junction. These are believed to create leakage paths which can discharge the node capacitor, causing loss of information.

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Trench Capacitor Modification to Improve Storage Time

      In one device capacitor storage memory cells made with trench
storage capacitor technology, failure of capacitor cells to hold or
retain stored charge has been correlated to the presence of crystal
defects emanating from the capacitor trenc h wall and passing through
the P-N node junction.  These are believed to create leakage paths
which can discharge the node capacitor, causing loss of information.

      These defects are generally found to start in the convex curved
region of the c apacitor trench, as shown in Fig. 1.  Modeling of the
forces generated by expa nsion of the polysilicon filling the
trenches in these regions shows that these are areas of maximum
tensile stress in the surrounding crystal silicon.

      The invention described here is a new design of the shape of
the trench storage capacitor in the region of intersection with the
P-N junction node, which reduc es the tensile stress in the crystal
silicon in this region.  The photolithograp hic mask used to produce
this new trench design is shown in Fig. 2a.  For com parison, the
original trench design is shown in Fig. 2b.

      Stress maps of the new trench design are shown in Fig. 3a and
the conventional trench design in Fig. 3b.  The reduced stress within
the trench - P-N junction intersection region with the new design is
evident.  Alternate rows of cells with the old and new trench design
were fabricated and analyzed for c...